Fully Biodegradable Superhigh Water Vapor Barrier PBAT Films with Diffusion-Impeded Interior Crystal Plates and a Superhydrophobic Rough Surface

Large-scale applications of biodegradable commodity polymers such as poly(butylene adipate- co -terephthalate) (PBAT) in food packaging and agricultural mulch films depend on the effective enhancement of gas and water vapor barrier properties. However, achieving a significant improvement in the water vapor barrier by at least 1 order of magnitude, which is highly desirable for mulch film applications in arid regions, remains a considerable challenge. In this study, an improvement of over one order of magnitude in the WV barrier property of PBAT was achieved through simple melt blending and hot pressing using long-chain saturated fatty acids (SFAs) as hydrophobic modifiers. SFAs with moderate hydrophobicity crystallized to form hydrophobic crystal plates with an aspect ratio of about ten both within the film interior and on the film surface. The crystal plates in the interior created highly tortuous paths, thereby impeding WV diffusion. Meanwhile, the crystal plates on the surface rendered the surface very rough (maximum roughness of 435 nm) and superhydrophobic (maximum water contact angle of 153 °), effectively reducing WV adsorption and dissolution. Through this mechanism, both the WV diffusion coefficient and solubility were simultaneously reduced, resulting in an enhancement of the WV barrier by over 40 times at most. Additionally, the thermal and mechanical properties of the films were assessed. This study provides a novel and practical approach to significantly improving water vapor barrier properties while maintaining full biodegradability.